wouter0100 / chronos

A standalone DateTime library originally based off of Carbon

CakePHP Chronos

Chronos aims to be a drop-in replacement for nesbot/carbon. It focuses on providing immutable date/datetime objects. Immutable objects help ensure that datetime objects aren't accidentally modified keeping data more predictable.

Installation

Installing with composer:

$ composer require cakephp/chronos

You can then use Chronos:

<?php
require 'vendor/autoload.php';

use Cake\Chronos\Chronos;

printf("Now: %s", Chronos::now());

Differences with nesbot/carbon

The biggest and main difference is that Chronos extends DateTimeImmutable instead of DateTime. Immutability for date values has proven to be a great way of avoiding bugs and reduce the amount of code, since developers don't have to manually copy the instance every time they need a change.

Another important feature it offers is the Date class, which is used for representing dates without time (calendar dates). Any time method called on this type of object is basically a no-op.

There are other implementation changes, but one that users might not notice is Chronos considers Monday as the start of the week instead of Sunday. This follows the ISO-8601 and current versions of PHP 5.6 and PHP 7.

A minor but still noticeable difference is that Chronos has no external dependencies, it is completely standalone.

Finally, Chronos is faster than Carbon as it has been optimized for the creation of hundreds of instances with minimal overhead.

Chronos also strives for HHVM compatibility, this library can be used safely with HHVM 3.11.

Migrating from Carbon

First add cakephp/chronos to your composer.json:

php composer.phar require cakephp/chronos

By default Chronos includes a compatibility script that creates aliases for the relevant Carbon classes. This will let most applications upgrade with very little effort. If you'd like to permanently update your code, you will need to update imports and typehints. Assuming src contains the files you want to migrate, we could use the following to update files:

# Replace imports
find ./src -type f -name '*.php' -exec sed -i '' 's/use Carbon\\CarbonInterval/use Cake\\Chronos\\ChronosInterval/g' {} \;
find ./src -type f -name '*.php' -exec sed -i '' 's/use Carbon\\Carbon/use Cake\\Chronos\\Chronos/g' {} \;

# Replace typehints and extensions
find ./src -type f -name '*.php' -exec sed -i '' 's/CarbonInterval/ChronosInterval/g' {} \;
find ./src -type f -name '*.php' -exec sed -i '' 's/Carbon/Chronos/g' {} \;

At this point your code should mostly work as it did before. The biggest difference is that Chronos instances are immutable.

Immutable Object Changes

Immutable objects have a number of advantages:

1. Using immutable objects is always free of side-effects.
2. Dates and times don't accidentally change underneath other parts of your code.

With those benefits in mind, there are a few things you need to keep in mind when modifying immutable objects:

// This will lose modifications
$date = new Chronos('2015-10-21 16:29:00');
$date->modify('+2 hours');

// This will keep modifications
$date = new Chronos('2015-10-21 16:29:00');
$date = $date->modify('+2 hours');

Getting Mutable Objects

In the case that you need a mutable instance you can get one:

$time = new Chronos('2015-10-21 16:29:00');
$mutable = $time->toMutable();

$date = new Date('2015-10-21');
$mutable = $date->toMutable();

Converting Mutable Objects into Immutable ones.

If you have a mutable object and want an immutable variant you can do the following:

$time = new MutableDateTime('2015-10-21 16:29:00');
$fixed = $time->toImmutable();

$date = new MutableDate('2015-10-21');
$fixed = $date->toImmutable();

Calendar Dates

PHP only offers datetime objects as part of the native extensions. Chronos adds a number of conveniences to the traditional DateTime object and introduces a Date object. Date instances offer compatibility with the ChronosInterface, but have their time frozen to 00:00:00 and the timezone set to the server default timezone. This makes them ideal when working with calendar dates as the time components will always match.

use Cake\Chronos\Date;

$today = new Date();
echo $today;
// Outputs '2015-10-21'

echo $today->modify('+3 hours');
// Outputs '2015-10-21'

Like instances of Chronos, Date objects are also immutable. The MutableDate class provides a mutable variant of Date.

Documentation

A more descriptive documentation can be found at book.cakephp.org/chronos/2/en/.

API Documentation

API documentation can be found on api.cakephp.org/chronos.